DESCRIPTION (Abstract of the application) The goal of this program is to develop a gene therapy approach for stable, efficient gene transfer to liver using retroviral vectors. Our preliminary data show that we can achieve gene transfer to liver with Moloney murine virus based retroviral vectors without prior toxic injury or surgical removal of hepatocytes, and that gene expression with reporter viruses persists for at least 9 months. This is accomplished by prior exposure of the liver to growth factors, and then subsequent i.v. infusion of high titer (>10e8 colony forming units/ml) retrovirus at the peak of hepatocyte proliferation. Additional preliminary data suggests that the growth factors to be studied, recombinant keratinocyte growth factor (rKGF) and recombinant hepatocyte growth factor (rHGF) induce different populations of hepatocytes to proliferate. Also, hepatocytes are responsive to a second exposure of rKGF. In the first aim of this proposal we will take advantage of these properties to optimize the levels of gene transfer that can be achieved using reporter viruses. In the second aim of this proposal experiments will be done to determine the potential therapeutic application of this method to the treatment of hyperlipidemia in low density lipoprotein receptor (LDLr) and apoprotein E (apoE)/LDLr double knock out (KO) mice. We have previously established biochemical and morphometric methods to quantitate alterations in lipid metabolism and atherosclerosis in these murine models. We will test the effects of LDLr gene transfer on cholesterol profiles, rate of VLDL and LDL clearance, and progression and severity of atherosclerotic disease. We hypothesize that a sufficient number of hepatocytes can be induced to proliferate with growth factors, subsequently allowing efficient gene transfer with retroviral vectors. We further hypothesize that LDLr gene replacement in murine models of hyperlipidemia will restore the ability of their hepatocytes to maintain normal plasma lipid profiles in vivo, preventing atherosclerosis. At the completion of these studies we will understand the level of gene transfer required to see a therapeutic response. Understanding the correlation between the number of transduced cells and modulation of disease severity is important in translating this approach to larger animal models, and ultimately, to humans.